Transfer function generator for providing a complex wave form of desired characteristics

ABSTRACT

A sine wave is split into positive and negative-going portions, the latter of which is inverted. Both half waves are now positive-going, and both are applied to a respective series of segmentator modules. These modules slice the sinusoidal half waves into strata of adjustable amplitude, and each linearly amplifies a respective stratum of variable gain. The outputs of the segmentators are combined in a differential amplifier to provide a complex wave form of desired characteristics.

United States Patent Inventor Eric Gschwmdtner North Tonawanda, N.Y. Appl. No 768,237 Filed Oct. 17, 1968 Patented July 27, 1971 Assignee The Wurlitzer Company Chicago, Ill.

TRANSFER FUNCTION GENERATOR FOR PROVIDING A COMPLEX WAVE FORM OF 230, 261; 328/13, 14, 22, 23, 28:31, 117, 146, 147, 187,142, 143;23s/197;s4/1.o1, 1.13, 1.26

[56] Relerenoes Cited UNITED STATES PATENTS 3,122,732 2/1964 Lewinstein et al 328/31 X 3,443,082 5/1969 Abe 235/197 3,482,169 12/1969 Peterson 328/142 X Primary ExaminerStanley D. Miller, Jr. Attorney-Olson, Trexler, Wolters and Bushnell ABSTRACT: A sine wave is split into positive and negativegoing portions, the latter of which is inverted. Both half waves are now positive-going, and both are applied to a respective series of segmentator modules. These modules slice the sinusoidal half waves into strata of adjustable amplitude, and each linearly amplifies a respective stratum of variable gain. The outputs of the segmentators are combined in a differential amplifier to provide a complex wave form of desired characteristics.

E8 .16 B6 .seansumron "ml/Li/ u 4 +5. 1 w 69 JZ .DIFFEKE'NT/AL v ANN/212R 1 PATENTEDMZYIQII SHEET 1 [IF 3 w i g 3 f ww AxQYV H Wm g MED: Qt

QSLZMMMKEQ 472 50 c/zwajmfim 5 01W, E/ZL, $01224 M PATENTEU JlJL27 I971 SHEET 3 OF 3 5 ww w V 2 w a E 9 W? R. m .M m u m F u 6 N FIIII .IllllllllllllllllllllllllllllL o a TRANSFER FUNCTION GENERATOR FOR PROVIDING A COMPLEX WAVE FORM OF DESIRED CHARACTERISTICS Most conventional musical instruments produce oscillations of rather complex wave form. In the'electronic musical art, wherein electronic organs are the primary example, it is often desired to simulate conventional musical instruments. Conventionally, there are two approaches to solution of the problem, which might respectively be termed additive and subtractive. As it is known from the Fourier theorum, any complex repeating wave form is a summation of a plurality of sine (or cosine) waves of different related periods and amplitudes.

In the additive form of synthesis, a plurality of sine waves is added together to simulate a complex wave. Although this is theoretically simple, in practice it is necessary to make substantial compromises. In order to hold costs to a a reasonable figure, and in order to hold a generating assembly to a reasonable size, the number of harmonics is limited to a relative few, and some of the harmonics are only approximated as to frequency. With this type of wave synthesis, tones that are not very rich in harmonics can be simulated fairly successfully. For example, flute tones are easily reproduced in this manner. However, more complex tones-as reeds or strings-are not very realistic.

The opposite approach is more often taken, namely, a wave form is generated which has all of the necessary harmonics to start with. For example, a sawtooth wave has all of the harmonies. A square wave has only add harmonics and thus is particularly useful for reproducing reed tones,v such as a clarinet, which have essentially only odd harmonics. The harmonics which are not desired for any particular tone then are filtered out. Again, however, practical problems are presented. For substantially perfect results, a rather large number of sharply tuned band-pass and band-elimination filters would be necessary. For cost and space reasons, compromises are practically universally made. Thus, the results are somewhat short of perfection, although the tones-particularly those of a complex nature-are generally much more realistic than those produced by synthesis or adding of sine waves.

In accordance with the present invention, neither of the foregoing approaches istaken. Rather, as in my prior application for U.S. Letters Patent, Ser. No. 577,203, filed Sept. 6, 1966, now U.S. Pat. No, 3,530,225 for Derivative and Synthesis of Musical Instrument Tones by Means of Non- Linear Transfer Function," a sine wave is applied to a transfer function device whose input-versus-output voltage characteristics can be adjusted into a variety of, nonlinear configurations. The transfer function generator forming the. subject matter of the present invention can transform asinusoidal input into a complex output wave form. The complexity of the output wave form, and hence the resultant tonal character, depends on the chosen nonlinearity and the. amplitude of the input. The frequency response of the device is. maintained appropriately flat to avoid noticeable phase shifts and amplitude deteriorations for input frequencies up to approximately kHz. The transfer function of the presentdevice comprises a continuous curve consisting of straight line segments. The curve goes through the origin, andcan traverseany of'the four quadrants of the input-output coordinates. The device comprises a plurality of segmentators which slice the input wave into various amplitude strata, and which variably process these strata. Each stratum is adjustable as to amplitude and as to gain, thereby allowing wide variation of the resultantoutput wave form.

Thus, it is an object of the present invention to provide a transfer function generator device in (which a cyclical input signal is sliced into a plurality of amplitude strata, the strata being individually processed and subsequentlyrecombined to form a complex output wave.

Although the primary object of the invention relates to a repetitive or cyclic signal, it is within the contemplation of the invention that a noncyclic input signal could be utilized, such as for the production of transient effects.

A further object of the present invention is to provide a transfer function generator in which an input signal is sliced into a plurality of amplitude strata with each stratum thereof processed by an individual stratum amplifier having gain factors which are adjustable between finite positive and negative limits.

Yet another object of the present invention is to provide a transfer function generator comprising a plurality of individual stratum amplifiers collectively providing an inputversus-output characteristic which is a continuous curve consisting of a plurality of straight line segments which are individually adjustable in their input coordinate projection and their slope.

Yet another object of the present invention is the provision of a transfer function generator wherein the input signal first split into its positive and negative components, the negative component then being inverted, and the two components thereafter being processed in substantially identical circuits.

Other and further objects and advantages of the present invention will be apparent from the following description, when taken in connection with the accompanying drawings, wherein:

FIG. I is a block diagram of a transfer function generator with a capacity of four straight line segments on either side of the origin;

FIG. 2 is a graph showing the transfer function and the relation of the input and output waves thereto;

FIG. 3 is a schematic wiring diagram of the signal conditioning part of the transfer function generator;

FIG. 4 is a circuit diagram ofone segmentator module forming a part of the present invention; and

FIG. 5 is a graph showing certain functions of the invention.

Turning now to the drawings in greater particularity, and first to FIG. 1, there will be seen an input wave 10 other wise identified as V0, illustrated as a sine wave. The wave 10 is supplied on an input line 12, and is split, going to an upper diode 14 which is poled to pass he positive-going half-wave, shown above the line 16 from the diode as a half sine wave with a plus sign therein. The input wave 10 also is applied to a lower diode 18 which is poled to pass the negative-going half-wave, shown below the line 20 to the right thereof as a half-sine wave, with a negative sign therein. This negative-going portion of the wave is applied to an inverter 22 which inverts the wave as shown above the line 24 leading from the inverter as a positive half-sine wave, but with a negative sign in it.

The positive-going half-wave, as indicated at S0 is applied to the input connection 26 of a succession of segmentator modules 28, respectively indicated as +81, +52, S3, and +84. The outputs of the segmentator modules as taken at 30 ase combined on a line 32 leading to a differential amplifier 34. The function and operation of the segmentator modules will be discussed shortly hereinafter.

Slmilarly, the negative-going portion of the input wave from the line 24, as indicated at -So, is applied to the input connection 36 of a series of similar segmentator modules 38, respectively identified as S1, S2, -S3, and -S4. As with the segmentator modules 28, there may be more or less than four of the segmentator modules 38. The outputs thereof, as taken at 40, are combined on a line 42 leading to the differential amplifier 34. The output wave of the differential amplifier appears on a line 44, and is shown somewhat suggestively as a sine wave, although it will be understood that in most instances it is a highly complex wave. Since the wave is of variable output characteristics, depending on adjustment of the segmentator modules 28 and 38, the exact shape cannot be shown, and the sinewave therefore is shown only to illustrate an alternating wave form.

The functionofthe segmentator modules 28'and also 38 is best seen with reference to FIG. 2. The modules slice the sinusoidal half waves +50 and So into strata of adjustable amplitude AX. The first of the segmentator modules 28, after taking the first stratum AXl, passes the remainder of the halfwave on to the second segmentator module +S2, and this takes away the second stratum AX2, passing on the remainder to the third sementator, etc. Seen in this manner, the segmentator modules are serially connected. I

In each segmentator module the stratum sliced off and retained is passed through an amplifier whose gain is settable between and 10 times. This gain setting determines the slope aof each segment of the transfer generator curve 46. In

FIG. 2 this curve will be seen to be a series of straight lines, there being one such straight line for each of the four segmentator modules 28. The curve portion 48 corresponding to the negative-going half-cycle of the input wave can be identical with that of the positive portion 46, but it need not be. Tracing the input wave 10 against the transfer function curve 46, 48, the output curve to the right will be seen to be generated as a very complex curve 50 having a portion 52 corresponding to the transfer function positive curve portion 46, and a portion 54 corresponding to the negative transfer function portion 48. Of course, it will be understood that the negative" portion is similar to the positive" portion except for the values of AX and or, since the negative-going portion of the input wave has been inverted before application thereto. Thus, the modules 28 and 38 are similar in design, differing only in their adjustment.

The output of the segmentator modules 28 as added together on the line 32 is indicated as Z+S(a, AX), while the output of the segmentator modules 38 as indicated on the line 42 is ES(a, AX). The two outputs (or groups of outputs) are respectively applied to the inverting and noninvertng inputs of a differential amplifier, and the output wave appearing at the output 44 is the processed and reconstituted complex wave form E+S(a, AX).

As will be apparent, the wave forms of FIG. 2 are plotted conventionally with the amplitude against time, amplitude of the output wave form being on the Y or vertical axis, and the amplitude of the input wave form being on the horizontal or X axis.

The block diagram of FIG. 1 is somewhat simplified, and some amplification thereof is shown in F IG. 3. Thus, the input wavelO-which, by way of exemplification, is of adjustable amplitude ranging from zero up to 5.0 volts RMS -is applied to the line 12, and from thence through a capacitor 56 and resistor 58 to an emitter follower transistor stage 60, with the output thereof being coupled by a capacitor 62 and a shunt resistor 64 to the diodes 14 and 18.

The diode 14 is connected to a junction 64 between the grounded resistor 66 and a capacitor 68 leading to the base of a transistor 70. The parallel combination of a diode 72 and resistor 74 is also connected to the base of the transistor 70, the diode being poled, as shown,'to conduct toward the base. The transistor 70 is in an emitter-follower circuit, with the output thereof being taken along line 16 to the various segmentator modules 28. The collector of the transistor 70 is connected to a positive supply line 76, and this is also connected to the col lector of the previously mentioned transistor 60.

The diode 72 and its associated RC components clamp the rectified halfwave form to a constant +24.0 volts supplied by an emitter follower mentioned hereinafter.

The reversely poled diode 18 likewise is connected to a junction between a grounded resistor 78 and a capacitor 80 leading to the base of a transistor 82. Also connected to this base is the parallel combination of a diode 84 and resistor 86, the diode being poled to conduct away from the base. It will be noted that, unlike the previously mentioned transistors, the transistor 82 is a PN P transistor, the output thereof being taken from the collector at unity gain, but inverted from the input as indicated at 88. This output is connected to the base of a transistor 90 having the collector thereof connected to the positive supply line 76. The transistor 90 comprises an emitter follower amplifier, and the output thereof is taken on the line 24 to the segmentator modules 38. The diode 84 and associated RC components likewise serve as a clamp for'the rectified half-wave form.

The diodes 72 and 84 are connected to a line 92 which is connected to a junction 94. The junction is connected to the emitter of NPN transistor 96, the collector of which is connected to the positive supply line 76. The base of this transistor is connected between a resistor 98 connected to the supply line and a grounded resistor. The junction 94 further is.

connected to a resistor 102 connected at a junction 104 in series with a grounded resistor 106. This circuit will be recognized as an active voltage regulation circuit, wherein the collector to emitter impedance of the transistor varies in accordance with the bias on the base, the latter being determined by the voltage divider, 98, and the voltage on the line 76. Thus, as noted heretofore, a constant +24.0 volts is supplied to the line 92. The clamp diodes 72, 84 and associated RC components prevent DC level shifts which would result from changes in input signal amplitudes.

The junction 104 is connected to the base of a transistor 108, the collector of which is connected to a line leading direct to the positive supply line 76. The emitter is connected to a grounded resistor 112, and further is connected to a positive regulated voltage line 114, supplying +1 1.4 volts to the segmentator modules 28 and 38. A regulated +40.0 volts also is supplied to the segmentator modules by way of a line 116 connected to the line 110.

The output lines 32 and 42 from the segmentator modules 38 are, as noted heretofore, connected to the differential amplifier 34. The differential amplifier comprises a PNP transistor 118 towhich the line 32 is connected at a junction 120. This junction is also connected to a resistor 122 leading to an. amplifier output junction 124. The collector of the transistor 118 is grounded, while the emitter is connected to the base of another PNP transistor 126, the collector of which is connected to the junction 124. 'The emitter of the transistor 126 is connected to a junction 128.

The junction 128 is connected to the collector of a transistor 130, the emitter of which is connected to a resistor 132 leading to a junction 134. A tab or slider 136 on the resistor 132 is connected to the junction 134. This comprises a potentiometer 138 for DC output balance. The base of the transistor is connected to a junction 140 having a grounded resistor 142 on one side thereof, and connected at the other side to a zener diode 144. The opposite side of the Zener diode is connected to a line 146 which is connected to a resistor 148 to the junction 134, and which is also connected to the junction 150 between the lines 110 and 116.

The junction 128 also is connected to the emitter of a PNP transistor 152, the collector of which is grounded. The base of this transistor is connected to the emitter of another PNP transistor 154, the collector of which is also grounded. The base of the transistor 154 is connected by means of a line 156 to a junction 158 between the line 42 and a pair of series esistors 160 and 162 leading to ground.

The reconstituted signal appears at the output 124, including the line 44, The line 44 is connected to the base of a transistor 164 for amplification of the signal.

The transistor 164 is a PNP transistor, and the emitter thereof is grounded. The collector is connected to a junction 166, and this is connected through a resistor 168 to a negative voltage supply line 170, preferably 39.0 volts. The junction 124 is connected through a resistor 172 to this line 170.

THe junction 166 also is connected to the anode of a zener diode 174, the cathode being connected to a junction 176. This zener diode reduces the DC level. This junction 176 is connected by means of a resistor 178 to the line 76, and also is connected to the base of a transistor 180 in an emitter follower output circuit. The transistor 180 is also a PNP transistor, the collector being connected to the negative line 170, and the emitter being connected to a line 182. The line 182 is provided with a DC output line 184 and an AC output line 186, and further is connected by means of a resistor 188 to the positive supply line 76. t

Circuit details of one segmentator module are to be seen in FIG 4. The input at 26 is connected by means of a capacitor 190 to the base of a transistor 192. This base is also connected by a parallel diode 194 and resistor 196 to a junction 198, the cathode of the anode being connected to the base of the transistor. The junction !98 is connected to the line 1 14 previously mentioned in connection with FIG. 3 to supply a constant ll.4 volts positive thereto. The transistor 192 is of the NPN type, and the collector is connected to a resistor 200 to a junction 202, which in turn is connected to the supply line 116 for providing a positive 40 volts. The emitter is grounded through a resistor 204, the output being taken from the emitter and applied to the stratum slicer comprising a resistor 206 connected to a junction 208, which in turn is connected to the anode of a diode 210. The transistor 192 may be considered as a low impedance driver for the stratum slicer. The stratum amplitude is determined by the DC voltage level at the emitter of a transistor 212 to which the cathode of the diode 210 is connected. The transistor 212 is an NPN transistor, and the emitter is connected to ground through a resistor 214. The collector is connected through a resistor 216 to a line 218 from the junction 202. The remainder of the input signal which is not sliced off by the stratum slicer 206, 210 appears on an output line 220 connected to the collector of transistor 212. The amplitude of the stratum sliced out is determined by the potential on the base of the transistor 212. This base is connected through a resistor 222 to a tap 224 on a potentiometer resistor 226. One end of this potentiometer resistor is connected through a resistor 228 to the 40 volt supply line 218, while the other end is connected through a resistor 230 to ground. The potential on the base of the transistor 212 is readily set by adjusting the position of the tap 224.

The emitter input impedance of transistor 212 is low, and thus represents a current sink which accepts the "remainder of the sliced half-wave. As noted, this remainder reappears at the collector of the transistor 212, which acts as a unity gain amplifier, and the remainder is passed on to the next segmentator. The retained stratum is applied to the input of a differential amplifier 232 comprising NPN transistors 234 and 236, Specifically, a line 238 leads from the junction 208 to the base of a transistor 240 which serves as a signal level in impedance transformer. The collector is connected through a resistor 242 to the line 218, while the emitter is connected to a junction 244 which is grounded through a resistor 246.

The junction 244 also is connected to a capacitor 247 paralleled by a resistor 248, the opposite end of which is connected to the base of the transistor 236. The top end of the parallel combination of capacitor-resistor is also connected through a resistor 250 to a junction 252, and this junction is connected through a resistor 254 to the 40 volt supply line 218.

The emitter of the transistor 236 is connected to a junction 256 which is grounded through a resistor 258. The junction also is connected to the emitter of the transistor 234, and the collector of this transistor is connected to a junction 258, and this junction is connected through a resistor 260 to the 40 volt line 218. The junction also is connected by means of a resistor 262 to the base of the transistor 234, and the base also is connected to a resistor 264 which is connected at a junction 266 to a grounded resistor 268, thereby providing DC bias for the base.

The junction 266 is connected to the emitter of an NPN transistor 270, the collector of which is connected through a resistor 272 to the positive supply line 218. The base of the transistor 270 is connected to a junction 274.

The junction 274 is connected through a resistor 276 to ground, and further is connected through a resistor 278 to a line 280 leading back to the junction 198.

As has been noted, transistor 240 serves as a signal level and impedance transformer. Transistor 270 does the same on the constant DC level input and is necessary to balance the temperature behavior of the circuit.

The junction 258 is connected to one side of a potentiometer resistor 282, the other side of'which isconnected back to the i act n 2. 6 l din p is provided on h pot ntiometer resistor 282, and is connected by means of a line 286 to the base of an NPN transistor 288. The potentiometer 282,

284 determines the gain from +10 to -l0, i.e., the slope, and hence is labeled 0:. Conversely. the potentiometer 224, 226 determines the amplitude of the stratum sliced out, and hence is labeled AX. The transistor 288 comprises an impedance transformer, and has its collector connected to the 40 volt supply line 218 and its emitter connected to a junction 290 which leads through a resistor 292 to ground, which also leads to an adding resistor 294 leading to the output line 32.

The capacitor 246, previously mentioned, compensates the input capacitance of transistor 236, and thus flattens the frequency response.

One segment is indicated in FIG. 5, comprising a generalized segment Sn=f(a1, AX). As will be seen, the slope at is indicated as an angle, and this can either plus or minus. The magnitude is indicated on the X axis, and comprises AX, as contemplated heretofore.

It will now be seen that l have disclosed practical circuit means for converting a simple input wave, such as a repeating sine wave, or a nonrepetitive pulse, into a complex output wave, the characteristics of which can be controlled as desired. The circuits have great utility in the synthetic production of musical tones, but are believed to have utility in other The specific embodiment of the invention as herein shown .'and described is for illustrative purposes only. Various changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of the present invention insofar as they fall within the spirit and scope of the appended claims.

lclaim:

1. A transfer function generator comprising means for receiving an input signal, means connected to said input signal receiving means for slicing the input signal into a plurality of amplitude strata, said slicing means comprising a plurality of threshold detectors of different threshold levels and each of which conducts when the input amplitude exceeds its threshold a plurality of amplifiers respectively connected to said slicing means for individually amplifying the strata, and combining amplifier means connected to said plurality of amplifiers for combining the outputs thereof to produce a complex output wave, the input-versus-output characteristic of said generator when represented in a Cartesian coordinate system being a continuous curve consisting of a plurality of straight line segments.

2. A transfer function generator as set forth in claim 1 wherein the slicing means includes means for individually adjusting the amplitude of each stratum sliced from the input signal.

3. A transfer function generator as set forth in claim 1 and further including means for adjusting the amplitude gain of each amplifier from finite positive to finite negative.

4. A transfer function generator as set forth in claim 2 and further including means for'adjusting the amplitude gain of each amplifier from finite positive to finite negative.

5. A transfer function generator as set forth in claim l wherein the input signal has both negative and positive portions, and wherein the receiving means includes means for inverting one of said portions so that both portions thereafter are of like sign.

7T1 transfer function generator as set forth in claim i wherein the combining amplifier is a differential amplifier.

8. A transfer function gerErator as'ffbiifiaaimi wherein each stratum amplifier comprises a differential ampli- 9. transfer function generator set 

1. A transfer function generator comprising means for receiving an input signal, means connected to said input signal receiving means for slicing the input signal into a plurality of amplitude strata, said slicing means comprising a plurality of threshold detectors of different threshold levels and each of which conducts when the input amplitude exceeds its threshold a plurality of amplifiers respectively connected to said slicing means for individually amplifying the strata, and combining amplifier means connected to said plurality of amplifiers for combining the outputs thereof to produce a complex output wave, the input-versus-output characteristic of said generator when represented in a Cartesian coordinate system being a continuous curve consisting of a plurality of straight line segments.
 2. A transfer function generator as set forth in claim 1 wherein the slicing means includes means for individually adjusting the amplitude of each stratum sliced from the input signal.
 3. A transfer function generator as set forth in claim 1 and further including means for adjusting the amplitude gain of each amplifier from finite positive to finite negative.
 4. A transfer function generator as set forth in claim 2 and further including means for adjusting the amplitude gain of each amplifier from finite positive to finite negative.
 5. A transfer function generator as set forth in claim 1 wherein the input signal has both negative and positive portions, and wherein the receiving means includes means for inverting one of said portions so that both portions thereafter are of like sign.
 6. A transfer function generator as set forth in claim 1 wherein the amplitude-to-frequency response characteristic is substantially flat.
 7. A transfer function generator as set forth in claim 1 wherein the combining amplifier is a differential amplifier.
 8. A transfer function generator as set forth in claim 1 wherein each stratum amplifier comprises a differential amplifier.
 9. A transfer function generator as set forth in claim 8 wherein each differential stratum amplifier includes a potentiometric voltage divider and the output is taken from a tap on said voltage divider.
 10. A transfer function generator as set forth in claim 1 wherein the signal slicing means includes a low output impedance driver. 